Tuberculosis (TB) is a global health problem resulting in 8 million new cases and 2 million deaths each year. The emergence of multi-drug and totally-drug resistant strains of TB only makes this problem more severe. The life cycle of Mtb has 3 stages. In the acute phase following initial infection the bacteria replicate in the host and virulence factors are expressed, leading to the generation of an immune response by the host. As the immune response begins to control the infection, the Mtb enters a latent, asymptomatic state in which the bacteria become non-replicating and are encased in granulomas. The bacterium can persist in this latent state in infected individuals for many years, making diagnosis and treatment of disease difficult. In some cases, the bacteria are reactivated and begin replicating again, leading back to the disease state. Reactivation can occur for numerous reasons, including immune suppression caused by diseases such as HIV, treatments such as chemotherapy, or the weakening of the immune system due to aging. An estimated 2 billion people are latently infected with Mtb worldwide, and reactivation of latent Mtb accounts for most new cases of active TB disease. Reactivation is associated with inflammation, necrosis and cavitation of the lung, a process that results in draining of the lesions into the bronchus. Aerosols generated when individuals with bronchial lesions cough causes dissemination of the Mtb organism to uninfected, susceptible persons, and the transmission cycle is thus maintained.
The only currently available vaccine against TB, Mycobacterium bovis (Bacille Calmette-Guërin) (BCG), was first introduced in 1921. BCG has been widely utilized and while studies show that for some purposes BCG is effective (e.g. against disseminated TB), it is known to be ineffective with respect to preventing the development, persistence and reactivation of latent TB. There is an ongoing need to develop improved, more effective vaccines against TB. In particular, there is a need to develop vaccines that provide protection against the development, maintenance and/or reactivation of latent tuberculosis infection. With the availability of the entire genomic sequence of Mtb, and the tools for bioinformatic and experimental analysis of Mtb antigens, many new potential Mtb vaccine candidates have been identified in recent years. These include antigens that are involved in acute infection, maintenance of latency, or reactivation of Mtb. There are a range of delivery strategies in clinical development that are comprised of combinations of these and other antigens that have been tested in animal models and are currently or will soon be in clinical trials.
While vaccines are often effective to immunize individuals prophylactically or therapeutically against pathogen infection or human diseases, there is a need for improved vaccines. There is also a need for compositions and methods that produce an enhanced immune response. Likewise, while some immunotherapeutics are useful to modulate immune response in a patient, there remains a need for improved immunotherapeutic compositions and methods.